For Magnetic Resonance Imaging (MRI), known examples of image taking methods used for taking images of a site having periodic motion include synchronization image taking processes performed in synchronization with a biological signal of an examined subject. A known example of the synchronization image taking processes is an electrocardiographic synchronization image taking process in which image taking processes are performed in synchronization with an electrocardiographic signal of the examined subject.
In this regard, methods used during electrocardiographic image taking processes include a prospective gating method and a retrospective gating method. The prospective gating method is a method by which pieces of data are acquired in a specific cardiac phase determined in advance. For example, according to the prospective gating method, timing of an R-wave is detected so as to repeatedly acquire pieces of data in various cardiac phases by using the R-wave as a trigger. In the prospective gating method, because there is a waiting time period prior to the occurrence of the trigger, it is necessary to perform repetitive image taking processes corresponding to two or more heartbeats, when taking images of the heart for a whole heartbeat. As a result, even when a four-fold speed-multiplying ratio is set by using a parallel imaging scheme together, for example, the substantial speed-multiplying ratio is only two-fold or less, because it is necessary to perform the repetitive image taking processes corresponding to two or more heartbeats.
The retrospective gating method is a method by which images are reconstructed by extracting pieces of data in mutually the same cardiac phase from among a series of data acquired in a sequential manner. For example, according to the retrospective gating method, the pieces of data are sequentially acquired without the synchronization with an electrocardiographic signal, and also an electrocardiographic signal during the data acquisition is obtained. Further, a reconstructing process is performed after rearranging the pieces of data in a retroactive manner so as to align the cardiac phases of the acquired series of data, by using the obtained electrocardiographic signal. By using the retrospective gating method, it is possible to shorten the image taking time period compared to that of the prospective gating method, because there is no need to wait for the trigger.